Thyroid hormones are critical for normal growth and development and for maintaining metabolic homeostasis. Yen (2001) Physiol. Rev. 81(3):1097-126. Circulating levels of thyroid hormones are tightly regulated by feedback mechanisms in the neuroendocrine axis (i.e., the HPT axis). Thyroid hormones exert profound effects on cardiac function, body weight, metabolism, metabolic rate, body temperature, cholesterol, bone, muscle, and behavior.
Subclinical thyroid diseases (e.g., subclinical hyperthyroidism and subclinical hypothyroidism) are common clinical entities that encompass mild degrees of thyroid dysfunction. The clinical significance of mild thyroid under-activity is uncertain, and therefore there is considerable controversy over the appropriateness of diagnostic testing and possible treatment of this condition. Cooper (2012) Lancet 379(9821):1142-54; Wilson & Curry (2005) AAFP 72(8). Subclinical hypothyroidism is typically defined as a serum thyroid-stimulating hormone (TSH) concentration above the statistically defined lower limit of the reference range, 0.45 to 4.50 μU/mL (0.45 to 4.50 mU/L), when serum free T4 thyroxine concentration are within its reference range. Subclinical hypothyroidism is associated with progression to overt disease. See, e.g., Wilson & Curry (2005).
Estimates of the incidence of subclinical hypothyroidism range between 3-8%. The incidence of subclinical hypothyroidism steadily increases with age, and it is more common in women than in men. Older adults are twice as likely to develop hypothyroidism as younger adults, the condition is commonly accompanied by symptoms including, for example, constipation, weight gain, dry and itchy skin, impaired cognitive function, and intolerance to cold.
Somatostatin (also known as growth hormone-inhibiting hormone (GHIH)) is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via its interaction with G-protein-coupled receptors and inhibition of the release of secondary hormones. For example, in the anterior pituitary gland, somatostatin inhibits the release of TSH and growth hormone.
It is well-established that intravenous (IV) administration of some amino acids results in significant inhibition of somatostatin; indeed this type of diagnostic testing for human growth hormone deficiency (another hormone regulated in part by somatostatin) (Merimee T J et al. N Engl J Med 1969;280:1434-1438; Alba-Roth J et al. J Clin Endocrinol Metab 1988;67:1186-1189). Other amino acids, such as methionine, phenylalanine, lysine, histidine, and ornithine have also led to marked increases in hGH (Alba-Roth, Muller, Schopohl, & von Werder, 1988; Chromiak & Antonio, 2002; Gourmelen, M., M. Donnadieu, et al. (1972) Ann Endocrinol (Paris) 33(5): 526-528).
Determination of an effective and safe oral functional blend that improves thyroid function in the general population with sub-clinical thyroid function is important to determine.
Symptoms such as cold hands and feet, sensitivity to cold, headaches, sleeplessness, coarse skin, swollen eyes, fragile nails, joint aches, constipation, fatigue, croaky voice, and dizziness are associated with subclinical hypothyroidism, and could be treated by improving thyroid function.
It would be desirable to provide a nutritional supplement for improving thyroid function, in particular an amino acid-containing composition that is well tolerated having the result of increasing or improving thyroid function in those individuals whose thyroid function has slowed as a function of increasing age (sub-clinical hypo-thyroid function) or otherwise desire thyroid support.